Hello, I use from Biorad Precision Plus Protein dual-color standard (MW marker), but the molecular weight that is estimated with this marker isn't usually precise. to confirm, I used from USP standard, but its MW didn't match again.
(I had this problem with different samples with different size, eg: 22 KD, 65 KD, and 150 KD).
There are many commercial prestained protein markers which are multicolored (Thermo Scientific and Invitrogen protein ladders). These ladders include selected bands that are green, orange or red. These alternative colors in the ladder provide unambiguous reference points for identifying which band corresponds to which molecular weight, even if some bands were run off the bottom of the gel.
Personally, I like Rainbow Markers (GE), where each marker protein has a different colour. That makes it easier to later plot the standard curve. In addition, you can see the markers already during electrophoresis, that helps in troubleshooting any problems that may occur. And you can also judge the transfer efficiency in Western blot without Ponceau staining.
Be aware, however, that SDS-PAGE only results in a crude estimate of molecular mass, 10% error is not unusual. A Ferguson plot is somewhat more reliable (see doi:10.1002/elps.1150091203 for a convenient setup), but if you really need exact masses, then non-electrophoretic methods would be preferable (MS, ultracentrifugation, LALLS, ...)
There are many commercial prestained protein markers which are multicolored (Thermo Scientific and Invitrogen protein ladders). These ladders include selected bands that are green, orange or red. These alternative colors in the ladder provide unambiguous reference points for identifying which band corresponds to which molecular weight, even if some bands were run off the bottom of the gel.
One of the molecular weight markers that I use the most is the GangNam-PINK Prestained Protein Ladder that contains 11 proteins in the range 10-175 kDa (iNtRON Biotechnology, Cat. No. 24053). I agree with Dr Buxbaum comment, these kind of markers only give an estimation of the apparent molecular mass.
My favorite prestained marker is NEB's Color marker P7719. However, I agree with the fact that prestained markers do not give an accurate MW determination, because the actual MWs of the different proteins is modified by the dye. Use an unstained ladder for more accurate MW determination.
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